JP2019014629A - Single crystal substrate, method for manufacturing the same and silicon carbide substrate - Google Patents

Abstract

To provide a single crystal substrate capable of forming a silicon carbide growth layer having less crystal defects even when the silicon carbide growth layer to be grown is thin; a method for manufacturing the single crystal substrate, capable of efficiently manufacturing the single crystal substrate; and a silicon carbide substrate including the high quality silicon carbide growth layer.SOLUTION: The single crystal substrate comprises: a base substrate having a plurality of grooves having a first crystal plane and second crystal plane, facing the first crystal plane, included on an inner surface and having an extending direction of a <110> direction, and a flat surface provided between the grooves; and a silicon carbide base film provided on the flat surface. The flat surface is preferably a Si {100} plane.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a single crystal substrate, a method for manufacturing a single crystal substrate, and a silicon carbide substrate.

  Silicon carbide (SiC) is a wide band gap semiconductor having a band gap (2.36 to 3.23 eV) that is twice or more that of Si, and has attracted attention as a material for high voltage devices.

  However, since SiC has a high crystallization temperature unlike Si, it is difficult to produce a single crystal ingot by a pulling method from a liquid phase similar to Si substrate. Therefore, a method of forming a SiC single crystal ingot by a sublimation method has been proposed. However, in such a sublimation method, it is very difficult to form a substrate having a large diameter and few crystal defects. On the other hand, cubic SiC (3C—SiC) among SiC crystals can be formed at a relatively low temperature, and therefore a method of performing epitaxial growth on a substrate has been proposed.

  As one method for producing an SiC substrate using this epitaxial growth, a heteroepitaxial technique for growing 3C—SiC on the Si substrate in the gas phase has been studied. For example, Non-Patent Document 1 discloses that an Si (100) substrate uses an offset substrate in which the [001] direction is inclined by about 4 ° to the [110] direction, and SiC is epitaxially grown on the surface thereof. . Thereby, in the SiC growth layer, it is possible to reduce crystal defects called anti-phase boundary (APB).

  Patent Document 1 includes a groove including a bottom portion of a (001) plane and a facet including a (111) plane, a (−1-11) plane, a (−111) plane, and a (1-11) plane. A semiconductor device having a semiconductor substrate provided, a semiconductor buffer layer provided on the semiconductor substrate, and a first semiconductor layer provided on the semiconductor buffer layer is disclosed.

Journal of Crystal Growth 78 (1986) 538-544.

JP 2006-166331 A

  However, the conventional offset substrate and the semiconductor substrate having a groove cannot sufficiently reduce crystal defects. In particular, when the SiC growth layer grown on the substrate is thin, the tendency becomes remarkable. For this reason, it is necessary to increase the thickness of the SiC growth layer, resulting in a decrease in manufacturing efficiency.

  An object of the present invention is to provide a single crystal substrate capable of forming a silicon carbide growth layer with few crystal defects even when the silicon carbide growth layer to be grown is thin, a method for producing a single crystal substrate capable of efficiently producing such a single crystal substrate, and An object of the present invention is to provide a silicon carbide substrate having a high-quality silicon carbide growth layer.

The above object is achieved by the present invention described below.
The single crystal substrate of the present invention includes a plurality of grooves having a first crystal face and a second crystal face opposite to the first crystal face on the inner surface and extending in the <110> direction, and between the grooves. A base substrate provided with a flat surface, and
A silicon carbide underlayer provided on the flat surface;
It is characterized by having.

  Thereby, since the silicon carbide growth layer can be grown using the silicon carbide underlayer as a seed layer, the silicon carbide growth layer can be efficiently and stably grown from the silicon carbide underlayer toward the groove. As a result, even when the silicon carbide growth layer to be grown is thin, a higher quality silicon carbide growth layer can be obtained.

In the single crystal substrate of the present invention, the flat surface is preferably a Si {100} surface.
Thereby, since a flat surface and a groove | channel can be formed with high precision, even when the silicon carbide growth layer to grow is thin, a crystal defect can be eliminated or reduced more efficiently.

  In the single crystal substrate of the present invention, the flat surface is preferably a surface in which the Si {100} plane is inclined at an angle of more than 0 ° and less than 54.7 ° in the <110> direction.

  Thereby, crystal defects can be eliminated or reduced not only in the grooves but also on the flat surface. As a result, a high-quality silicon carbide growth layer with fewer crystal defects can be formed.

  In the single crystal substrate of the present invention, the angle formed between the flat surface and the first crystal surface is preferably larger than the angle formed between the flat surface and the Si {111} surface.

  Thereby, crystal defects can be associated with higher probability, and can be eliminated or reduced.

In the single crystal substrate of the present invention, the base substrate preferably contains silicon, polycrystalline silicon carbide, or diamond.
Thereby, a higher quality silicon carbide growth layer can be formed.

The method for producing a single crystal substrate of the present invention is a method for producing a single crystal substrate of the present invention,
Preparing a base material with a mask comprising a single crystal base material and a mask provided on a part of the surface of the single crystal base material;
Forming the silicon carbide underlayer on the surface of the single crystal base material;
Etching the single crystal base material to form the groove;
Removing the mask;
It is characterized by having.
Thereby, a single crystal substrate can be manufactured efficiently.

The silicon carbide substrate of the present invention, the single crystal substrate of the present invention,
A silicon carbide growth layer formed on the single crystal substrate;
It is characterized by having.

  Thereby, a silicon carbide substrate provided with a semiconductor layer capable of forming a power device is obtained by utilizing the wide band gap of the silicon carbide growth layer and the small number of crystal defects.

It is a longitudinal cross-sectional view of the silicon carbide substrate which concerns on this embodiment. FIG. 2 is a perspective view showing a single crystal substrate included in the silicon carbide substrate shown in FIG. 1. FIG. 3 is a perspective view showing only a base substrate included in the single crystal substrate shown in FIG. 2. FIG. 2 is an enlarged view of the silicon carbide substrate shown in FIG. 1, schematically showing an example of crystal defects. It is a figure for demonstrating embodiment of the manufacturing method of the single crystal substrate of this invention. It is a figure for demonstrating embodiment of the manufacturing method of the single crystal substrate of this invention. It is a figure for demonstrating embodiment of the manufacturing method of the single crystal substrate of this invention. It is a figure for demonstrating embodiment of the manufacturing method of the single crystal substrate of this invention. It is a figure for demonstrating embodiment of the manufacturing method of the single crystal substrate of this invention.

  Hereinafter, a single crystal substrate, a method for manufacturing a single crystal substrate, and a silicon carbide substrate will be described in detail based on preferred embodiments shown in the accompanying drawings.

<Silicon carbide substrate>
First, an embodiment of a silicon carbide substrate of the present invention will be described.

FIG. 1 is a longitudinal sectional view of a silicon carbide substrate 10 according to the present embodiment.
A silicon carbide substrate 10 (an embodiment of the silicon carbide substrate of the present invention) includes a single crystal substrate 1 (an embodiment of the single crystal substrate of the present invention), a silicon carbide growth layer 4 formed on the single crystal substrate 1, and ,have. This silicon carbide growth layer 4 is used, for example, as a semiconductor layer capable of forming a power device to be described later, taking advantage of its wide band gap and few crystal defects.

  An example of the silicon carbide growth layer 4 is a semiconductor layer made of cubic silicon carbide (3C—SiC). Cubic silicon carbide has a wide band gap value of 2.36 eV or more, and has a high thermal conductivity and high breakdown electric field, so that it is particularly preferably used as a wide band gap semiconductor for power devices. In addition, the silicon carbide growth layer 4 is not limited to the semiconductor layer comprised by 3C-SiC, The semiconductor layer comprised by 4H-SiC and 6H-SiC may be sufficient.

  By using the single crystal substrate 1 described later, a high quality silicon carbide growth layer 4 with few crystal defects can be formed.

  In addition, as a power device manufactured using the silicon carbide substrate 10, the transistor, diode, etc. for boost converters are mentioned, for example. Specific examples include a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), and a Schottky barrier diode (SBD).

Hereinafter, the single crystal substrate 1 will be described in more detail.
(Single crystal substrate)
FIG. 2 is a perspective view showing single crystal substrate 1 included in silicon carbide substrate 10 shown in FIG. FIG. 3 is a perspective view showing only the base substrate 2 included in the single crystal substrate 1 shown in FIG.

  Single crystal substrate 1 has a base substrate 2 and a silicon carbide base film 3 provided on base substrate 2. Such a single crystal substrate 1 is used, for example, as a base for epitaxially growing the silicon carbide growth layer 4 using the silicon carbide base film 3 as a seed layer.

-Underlying substrate-
The base substrate 2 is not particularly limited as long as it is a single crystal substrate. For example, these crystals are formed on a silicon substrate, a polycrystalline silicon carbide substrate, a diamond substrate, a sapphire substrate, a quartz substrate, or an arbitrary substrate. It is a composite substrate.

  Among these, the base substrate 2 preferably contains silicon, polycrystalline silicon carbide, or diamond, and more preferably is composed of a crystal material mainly containing these. Such a base substrate 2 contains cubic crystals, and is suitable as a base for growing silicon carbide. For this reason, by using this base substrate 2, a higher quality silicon carbide growth layer 4 can be formed.

  The thickness of the base substrate 2 is appropriately set so as to have a mechanical strength that can withstand the handling in the process of forming the silicon carbide growth layer 4, but is preferably about 100 μm or more and 2 mm or less as an example.

  As an example, the base substrate 2 shown in FIG. 1 is a single crystal silicon substrate having a principal surface of Si (001). The lower surface 2a of the base substrate 2 is a flat surface of the Si (001) surface. On the other hand, the upper surface 2b of the base substrate 2 includes a plurality of flat surfaces 21 made of a Si (001) surface and a plurality of grooves 22 whose extending direction is the [110] direction. That is, on the upper surface 2b, a plurality of flat surfaces 21 extending in the [110] direction and a plurality of grooves 22 extending in the [110] direction are alternately arranged in a direction orthogonal to the [110] direction. . Thereby, the upper surface 2b has a concavo-convex shape in which convex portions (mountains) having the flat surface 21 as a top surface and concave portions (valleys) formed of the grooves 22 are alternately arranged along the [1-10] direction. It is a surface.

  Here, each groove 22 has a V-shaped cross section. That is, each groove 22 includes a first crystal face 221 and a second crystal face 222 opposite to the first crystal face 221 on the inner surface. Each groove 22 extends in the [110] direction while maintaining such a V-shaped cross-sectional shape constituted by the first crystal face 221 and the second crystal face 222. Note that the first crystal plane 221 and the second crystal plane 222 are opposed to each other is located on the inner surface of the groove 22 and on the opposite sides of the bottom of the groove 22. Say.

  Note that the opening angle θ of the groove 22, that is, the angle formed by the first crystal face 221 and the second crystal face 222 is preferably more than 70.6 °. The groove 22 having such an opening angle θ efficiently eliminates or reduces crystal defects in the silicon carbide crystal when silicon carbide is epitaxially grown on the single crystal substrate 1 including the groove 22 on the upper surface 2b. be able to. Thereby, a high quality silicon carbide growth layer 4 is obtained.

  Here, FIG. 4 is an enlarged view of the silicon carbide substrate 10 shown in FIG. 1, and is a diagram schematically showing an example of a crystal defect.

  In the groove 22, as described above, the first crystal face 221 and the second crystal face 222 face each other. In the example shown in FIG. 4, the crystal defect 91 starting from the first crystal plane 221 progresses in parallel with the Si (111) plane. On the other hand, the crystal defects 92 originating from the second crystal plane 222 have progressed parallel to the Si (1-11) plane. Then, the crystal defect 91 and the crystal defect 92 are associated at the meeting point 93 and disappear. As described above, in the silicon carbide growth layer 4 grown on the single crystal substrate 1 having the groove 22, the crystal defects 91 and 92 that propagate in different directions can be associated with each other and eliminated or reduced.

  When the opening angle θ of the groove 22 is less than the lower limit value, the opening angle θ is too narrow, so that the probability that the crystal defects 91 and 92 are associated with each other decreases, and the crystal defects 91 and 92 cannot be sufficiently reduced. There is a fear.

  Further, the opening angle θ of the groove 22 is more preferably 100 ° or more and 176 ° or less, further preferably 150 ° or more and 175 ° or less, and particularly preferably 166 ° or more and 174 ° or less. Thereby, the crystal defects 91 and 92 can be eliminated or reduced more efficiently. If the opening angle θ of the groove 22 exceeds the upper limit value, the effect of providing the groove 22 is diminished, so that the probability that the crystal defects 91 and 92 meet is reduced, and the crystal defects 91 and 92 are sufficiently removed. There is a possibility that it cannot be reduced.

  The opening angle θ of the groove 22 can be adjusted according to the width of the groove 22, the formation time of the groove 22, and the like. For example, by increasing the width of the groove 22, the opening angle θ of the groove 22 can be increased. On the other hand, by reducing the width of the groove 22, the opening angle θ of the groove 22 can be decreased. Moreover, since the groove 22 can be deepened by lengthening the formation time of the groove 22, the opening angle θ of the groove 22 can be reduced, while the groove 22 can be formed by shortening the formation time of the groove 22. Since 22 can be shallow, the opening angle θ of the groove 22 can be increased.

  As described above, the groove 22 extends in the [110] direction. The base substrate 2 has a plurality of grooves 22 that are arranged in a direction orthogonal to the [110] direction.

  On the other hand, the base substrate 2 according to the present embodiment has a Si (001) surface as the flat surface 21 provided between the adjacent grooves 22 as described above. By providing such a flat surface 21, the upper surface 2 b of the base substrate 2 becomes a surface on which the groove 22 can be easily processed. Therefore, the concavo-convex shape in which the flat surface 21 and the groove 22 are alternately arranged with high accuracy. It becomes the surface which has. Such upper surface 2b can eliminate or reduce crystal defects more efficiently even when the silicon carbide growth layer 4 grown on the single crystal substrate 1 is thin.

  Further, the flat surface 21 according to the present embodiment is a region for forming the silicon carbide base film 3 described above. That is, by providing the flat surface 21, the silicon carbide base film 3 can be stably provided adjacent to the groove 22. Thereby, since the silicon carbide growth layer 4 can be grown using the silicon carbide underlayer 3 as a seed layer, the silicon carbide growth layer 4 can be efficiently and stably grown from the silicon carbide underlayer 3 toward the groove 22. Can do. As a result, even when the silicon carbide growth layer 4 to be grown is thin, a higher quality silicon carbide growth layer 4 can be obtained.

  The flat surface 21 may be parallel to the lower surface 2a (back surface) or may be non-parallel. In the case of being parallel, it is easy to provide the silicon carbide undercoat film 3 having a uniform thickness with respect to the flat surface 21, so that the silicon carbide growth layer 4 that grows toward the groove 22 also has few crystal defects. It is done.

  In addition, the angle α formed by the flat surface 21 and the first crystal surface 221 is preferably larger than the angle formed by the flat surface 21 and the Si (1-11) surface. Since the Si (1-11) plane is a plane parallel to the crystal defects, the angle formed by the flat surface 21 and the first crystal plane 221 is larger than the angle formed by the Si (1-11) plane. By setting, crystal defects can be associated with higher probability, and can be eliminated or reduced.

  Further, the angle formed between the flat surface 21 and the second crystal surface 222 is the same as the angle formed between the flat surface 21 and the first crystal surface 221.

  Further, FIG. 1 illustrates an example in which the flat surface 21 is a Si (001) surface, but the flat surface 21 is not limited to this surface, and the Si (001) surface is inclined at a predetermined angle. It may be a surface. As an example, a surface in which the Si (001) plane is inclined at an angle of more than 0 ° and less than 54.7 ° in the [110] direction can be given. By setting the inclined surface as the flat surface 21, crystal defects can be eliminated or reduced not only in the groove 22 but also in the flat surface 21. As a result, it is possible to form a high quality silicon carbide growth layer 4 with fewer crystal defects.

  The inclination angle from the Si (001) plane is more preferably 1 ° or more and 15 ° or less, and further preferably 2 ° or more and 10 ° or less. Thereby, the said effect becomes more remarkable and the further quality improvement of the silicon carbide growth layer 4 is achieved.

  The period C of the groove 22 (see FIG. 4), that is, the total of the width W2 of the groove 22 and the width W1 of the flat surface 21 is not particularly limited, but is preferably 0.1 μm to 100 μm, preferably 0.2 μm More preferably, it is 20 μm or less. By setting the period C of the groove 22 within the above range, crystal defects can be eliminated or reduced more efficiently even when the silicon carbide growth layer 4 grown on the single crystal substrate 1 is thin.

  The width W2 of the groove 22 is preferably 5% to 95% of the period C of the groove 22, and more preferably 30% to 85%. By setting the ratio of the width W2 of the groove 22 to the period C of the groove 22 within the above range, the balance between the width W2 of the groove 22 and the width W1 of the flat surface 21 is optimized. As a result, even when the silicon carbide growth layer 4 grown on the single crystal substrate 1 is thin, crystal defects can be eliminated or reduced more efficiently.

  When the single crystal constituting the base substrate 2 is a cubic crystal, for example, (001) plane, (010) plane, (001) plane, (−100) plane, (0-10) plane, (00−) 1) A surface etc. are mutually equivalent surfaces. Therefore, the Si (001) plane in the present specification can be replaced by these equivalent planes. That is, since the Si (001) plane in the present invention is not limited to only that plane, when these equivalent planes are collectively described, they are typically described as Si {100} planes. In the present specification, it is described that there is a predetermined relationship between the Si (001) plane and other planes and directions. However, when the Si (001) plane is replaced with an equivalent plane. The other surfaces and directions are also replaced so that the predetermined relationship described above is maintained.

  Similarly, for example, the (111) plane, the (−111) plane, the (1-11) plane, the (11-1) plane, the (−1-11) plane, the (-11-1) plane, and the like are equivalent to each other. This is a serious aspect. Therefore, since the Si (111) plane and the Si (1-11) plane in this specification can be replaced with these equivalent planes, in the present application, when these equivalent planes are collectively described, It is described as a Si {111} plane. In this specification, it is described that there is a predetermined relationship between the Si (111) plane or the Si (1-11) plane and other planes or directions. 1-11) When a plane is replaced with an equivalent plane, other planes and directions are also replaced so that the predetermined relationship described above is maintained.

  Similarly, for example, the [110] direction, the [101] direction, the [011] direction, the [1-10] direction, the [10-1] direction, the [01-1] direction, and the like are mutually equivalent directions. Therefore, the [110] direction and the [1-10] direction in the present specification can be replaced with these equivalent directions. Therefore, in the present application, when these equivalent directions are collectively described, typically <110 > Direction. In the present specification, it is described that there is a predetermined relationship between the [110] direction and the [1-10] direction and other surfaces and directions, but the [110] direction and [1-10] When the direction is replaced with an equivalent direction, other surfaces and directions are also replaced so that the predetermined relationship described above is maintained.

-Silicon carbide underlayer-
The silicon carbide base film 3 is provided on the flat surface 21 in the upper surface 2 b of the base substrate 2. The silicon carbide base film 3 may be, for example, a carbide film obtained by modifying the surface of a silicon single crystal substrate, or a silicon carbide film obtained by forming SiC on the upper surface of the base substrate 2. Also good. Further, the silicon carbide base film 3 may be provided only on a part of the flat surface 21.

  Although the crystal structure of the silicon carbide underlayer 3 is not particularly limited, for example, cubic SiC (3C—SiC) is used. Note that crystals other than 3C—SiC, such as 4H—SiC and 6H—SiC, may be used.

  Moreover, the thickness of the silicon carbide underlayer 3 is not particularly limited, but is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more and 50 nm or less, and further preferably 3 nm or more and 10 nm or less. By setting the thickness of the silicon carbide underlayer 3 within the above range, the thickness becomes necessary and sufficient for the seed layer.

  Note that if the thickness of the silicon carbide underlayer 3 is less than the lower limit, the thickness of the silicon carbide underlayer 3 may be insufficient as a seed layer. On the other hand, if the thickness of the silicon carbide underlayer 3 exceeds the upper limit, the thickness of the silicon carbide underlayer 3 becomes too thick. There is a risk of reaching the layer 4.

  Further, the thickness of the silicon carbide underlayer 3 is measured, for example, by a measurement method using an optical technique such as ellipsometry, or the cross section of the single crystal substrate 1 is observed with an electron microscope, an optical microscope, etc. It is calculated | required by methods, such as measuring the thickness of the silicon carbide base film 3 on an observation image.

  Further, the silicon carbide underlayer 3 is preferably a single crystal as a whole, but is not necessarily limited thereto, and may be polycrystalline, microcrystalline, or amorphous.

  The silicon carbide underlayer 3 may be provided not only on the flat surface 21 but also in the groove 22, that is, at least a part of the first crystal surface 221 and the second crystal surface 222, but is preferably a flat surface. 21 only. Thereby, since the crystal can be grown toward the inside of the groove 22 using the silicon carbide underlayer 3 provided at a constant density as a seed layer, a crystal with fewer crystal defects can be grown. As a result, a higher quality silicon carbide growth layer 4 can be obtained.

<Method for producing single crystal substrate>
Next, an embodiment of a method for producing a single crystal substrate of the present invention will be described.

  5 to 9 are diagrams for explaining embodiments of the method for producing a single crystal substrate of the present invention.

  The method for manufacturing the single crystal substrate 1 according to the present embodiment includes a step of preparing a base material 120 with a mask including the single crystal base material 100 and a first mask 110 provided on a part of the surface, and a single crystal There are a step of providing the second mask 30 on the surface of the base material 100, a step of etching the single crystal base material 100 to form the groove 22, and a step of removing the first mask 110. According to such a manufacturing method, the single crystal substrate 1 can be manufactured efficiently. Hereinafter, each process will be described sequentially.

[1] First, a single crystal base material 100 is prepared. Since the single crystal base material 100 is a raw material for the base substrate 2, for example, the same single crystal material as that for the base substrate 2 described above can be used.

  Next, a mask coating 110 ′ is provided on the surface of the single crystal base material 100. Here, first, a mask film 110 ′ is formed so as to cover the entire surface of the single crystal base material 100 (see FIG. 5). The mask coating 110 ′ is made of a material having resistance in the etching process of the single crystal base material 100 described later. Examples of such materials include silicon oxide and silicon nitride.

  Next, a photosensitive coating is formed on the surface of the mask coating 110 '. Then, this photosensitive film is subjected to patterning by exposing and developing. Thereby, the resist film 130 provided only in the target region is obtained (see FIG. 5).

Next, the mask coating 110 ′ is etched through the patterned resist film 130. Thereby, a region of the mask coating 110 ′ that is not covered with the resist film 130 is etched. As a result, the first mask 110 provided in the region corresponding to the groove 22 to be formed in the process described later is obtained (see FIG. 6). And mask base material 120 provided with single crystal base material 100 and 1st mask 110 provided in a part of the surface is obtained.
Thereafter, the resist film 130 is removed.

[2] Next, as shown in FIG. 7, a second mask 30 is formed on the surface of the single crystal base material 100. The second mask 30 is formed in a region of the surface of the single crystal base material 100 that is not covered with the first mask 110. The second mask 30 may be formed on the surface of the first mask 110, but is omitted in FIG.

  The method for forming the second mask 30 is not particularly limited. For example, the second mask 30 is formed by modifying (carbonizing) the surface of the single crystal base material 100, or silicon carbide is formed on the upper surface of the single crystal base material 100. And the like.

  The carbonization treatment is performed by heating the single crystal base material 100 in a carbon-based gas atmosphere. According to the carbonization treatment, since a part of the single crystal base material 100 is converted into silicon carbide, it is possible to form the second mask 30 having higher crystallinity than other methods.

The carbon-based gas atmosphere is composed of a processing gas containing a carbon-based gas. The carbon-based gas is not limited as long as it contains carbon. For example, in addition to ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), propane (C ₃ H ₈ ), methane (CH ₄ ) Hydrocarbon gases such as ethane (C ₂ H ₆ ), normal butane (n-C ₄ H ₁₀ ), isobutane (i-C ₄ H ₁₀ ), neopentane (neo-C ₅ H ₁₂ ), etc. 1 type or 2 types or more can be used in combination.

  Further, it may be a mixed gas of these hydrocarbon gases and other gases. Examples of the other gas include hydrogen silicide-based gas, silicon chloride-based gas, and silicon carbide-based gas.

  Furthermore, any gas such as a carrier gas may be mixed with these processing gases. Examples of the carrier gas include hydrogen, nitrogen, helium, and argon. When a carrier gas is used, the concentration of the carbon-based gas in the processing gas is appropriately set according to the speed of carbonization, etc., but as an example, it is preferably 0.1% by volume to 30% by volume, More preferably, it is 0.3 volume% or more and 5 volume% or less.

  The heating temperature of the single crystal base material 100 in the carbonization treatment is preferably 500 ° C. or higher and 1400 ° C. or lower, more preferably 800 ° C. or higher and 1300 ° C. or lower, and further preferably 950 ° C. or higher and 1200 ° C. or lower. . The heating time of the single crystal base material 100 in the carbonization treatment is preferably 0.5 minutes or more, more preferably 1 minute or more and 120 minutes or less, and more preferably 3 minutes. More preferably, it is 90 minutes or less.

  By setting the heating condition within the above range, the second mask 30 having the thickness as described above can be formed. Moreover, since the conversion rate to silicon carbide is optimized by optimizing the applied thermal energy, the second mask 30 with good quality can be formed.

  The carbonization treatment may be performed in any of a normal pressure atmosphere, a pressurized atmosphere, and a reduced pressure atmosphere, but preferably in a state in which a processing gas is introduced while exhausting the processing chamber containing the single crystal base material 100. You just have to do it. As an example, the introduction amount of the carbon-based gas in the processing gas is set to 10 sccm or more and 100 sccm or less.

  On the other hand, in the film forming process of silicon carbide, for example, a vapor phase film forming method such as a CVD method or a vapor deposition method is used.

[3] Next, the single crystal base material 100 is etched. Thereby, the groove 22 is formed.
In this etching process, the upper surface of the single crystal base material 100 is etched so that the lower portion of the first mask 110 (region facing the first mask 110) is removed.

  Examples of such an etching process include a process of heating the masked base material 120 provided with the second mask 30 at a temperature equal to or higher than the sublimation temperature of Si. As a result, Si atoms contained in the single crystal base material 100 are easily sublimated, and are discharged to the outside through the gap between the single crystal base material 100 and the first mask 110. As a result, the lower portion of the first mask 110 is etched to form the groove 22 as shown in FIG.

  The heating temperature varies slightly depending on the pressure of the space in which the single crystal base material 100 is placed, but is a temperature at which Si atoms can sublime and a temperature not higher than the melting point of Si, and not lower than 900 ° C. and not higher than 1400 ° C. Any range is acceptable. Moreover, although heating time is set timely according to the said heating temperature, it is preferable that the time exposed to heating temperature is 0.5 to 60 minutes.

  Further, the heating of the base material with mask 120 may be performed in a normal pressure atmosphere or a pressurized atmosphere, but is preferably performed in a reduced pressure atmosphere or a reducing atmosphere. Thus, sublimation of Si atoms is promoted and oxidation is prevented, so that the etching process can be performed while suppressing the modification of the single crystal base material 100.

The pressure in the reduced-pressure atmosphere is not particularly limited as long as it is less than atmospheric pressure, but it is, for example, 0.5 Pa or less.
As described above, the groove 22 is formed below the first mask 110.

  Note that etching is suppressed in a region where the second mask 30 is formed on the upper surface of the single crystal base material 100. For this reason, the flat surface 21 mentioned above will be formed in this area | region.

  In the etching process, a process of exposing the masked base material 120 provided with the second mask 30 to an etching gas may be used instead of the above heat treatment.

[4] Next, the first mask 110 is removed.
For example, an etching process is used to remove the first mask 110.

  The single crystal substrate 1 shown in FIG. 9 is obtained as described above. The second mask 30 shown in FIG. 9 can be used as the silicon carbide base film 3 shown in FIG. For this reason, the second mask 30 may be removed, but may be left without being removed.

<Method for producing silicon carbide substrate>
Next, an example of a method for manufacturing the silicon carbide substrate 10 shown in FIG. 1 will be described.

  Silicon carbide substrate 10 is manufactured by epitaxially growing silicon carbide growth layer 4 on single crystal substrate 1. The silicon carbide base film 3 functions as a seed layer for epitaxially growing the silicon carbide growth layer 4.

  The silicon carbide growth layer 4 is grown, for example, by containing the single crystal substrate 1 in a processing chamber and heating the single crystal substrate 1 while introducing a raw material gas, thereby using the silicon carbide underlayer 3 as a seed layer. As a result, silicon carbide substrate 10 shown in FIG. 1 is obtained.

  As the source gas, a mixed gas obtained by mixing a gas containing carbon and a gas containing silicon at a predetermined ratio, carbon containing carbon and silicon at a predetermined ratio, a gas containing silicon, and a gas containing carbon Examples of the mixed gas include a gas containing silicon and a gas containing carbon and silicon mixed at a predetermined ratio.

Among these, as gas containing carbon, for example, acetylene (C ₂ H ₂ ), propane (C ₃ H ₈ ), methane (CH ₄ ), ethane (C ₂ H ₆ ) in addition to ethylene (C ₂ H ₄ ). ), Normal butane (n-C ₄ H ₁₀ ), isobutane (i-C ₄ H ₁₀ ), neopentane (neo-C ₅ H ₁₂ ), etc., and a combination of one or more of these Can be used.

Examples of the gas containing silicon include monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), trisilane (Si ₃ H ₈ ), tetrasilane (Si ₄ H ₁₀ ), dichlorosilane (SiH ₂ Cl ₂ ), Tetrachlorosilane (SiCl ₄ ), trichlorosilane (SiHCl ₃ ), hexachlorodisilane (Si ₂ Cl ₆ ) and the like can be mentioned, and one or more of these can be used in combination.

Furthermore, examples of the gas containing carbon and silicon include methylsilane (SiH ₃ CH ₃ ), dimethylsilane (SiH ₂ (CH ₃ ) ₂ ), trimethylsilane (SiH (CH ₃ ) ₃ ), and the like. One kind or a combination of two or more kinds can be used.

  The heating temperature in epitaxial growth, that is, the temperature of the single crystal substrate 1 during epitaxial growth is preferably 600 ° C. or higher and 1400 ° C. or lower, more preferably 800 ° C. or higher and 1350 ° C. or lower, and 950 ° C. or higher and 1100 ° C. More preferably, it is as follows. In addition, the heating time in epitaxial growth is suitably set according to the target thickness of the silicon carbide growth layer 4.

Moreover, the pressure in the processing chamber in the epitaxial growth is not particularly limited, but is preferably 1 × 10 ⁻⁴ Pa or more and atmospheric pressure (100 kPa) or less, and more preferably 1 × 10 ⁻³ Pa or more and 10 kPa or less.

  By epitaxially growing silicon carbide growth layer 4 on silicon carbide underlayer 3 as described above, silicon carbide substrate 10 having high-quality silicon carbide growth layer 4 can be obtained efficiently.

  Such a high-quality silicon carbide substrate 10 is suitably used as a semiconductor substrate capable of manufacturing a high-performance power device, for example.

  The single crystal substrate, the method for manufacturing the single crystal substrate, and the silicon carbide substrate according to the present invention have been described based on the illustrated embodiment, but the present invention is not limited to this. For example, the single crystal substrate and the silicon carbide substrate according to the present invention may be obtained by adding arbitrary elements to the above-described embodiments. In addition, the method for manufacturing a single crystal substrate according to the present invention may be obtained by adding an arbitrary step to the above-described embodiment.

Next, specific examples of the present invention will be described.
1. Production of silicon carbide substrate (Example 1)
<1> First, a 6-inch (150 mm diameter, 0.625 mm thick) silicon wafer having a Si (001) surface as a main surface was prepared as a single crystal base material. Then, the surface was washed with hydrofluoric acid or the like.

  Next, a mask film was formed on the entire surface of the silicon wafer. Subsequently, after a resist film was formed on the mask film, the mask film was etched. Thereby, the base material with a mask which has the 1st mask patterned by the target shape was obtained.

  <2> Next, a second mask was formed on the surface of the base material with a mask. In forming the second mask, ethylene gas was used, and the surface of the silicon wafer was carbonized by heating at 1000 ° C. for 60 minutes.

  <3> Next, the base material with a mask provided with the second mask was etched. As a result, a base substrate in which grooves extending in the [011] direction and flat surfaces were alternately arranged was obtained. In this etching process, the masked base material was heated at 1000 ° C. for 30 minutes in a reduced pressure atmosphere.

  <4> Next, the first mask was removed by etching. As a result, a single crystal substrate including the base substrate and the second mask was obtained.

  <5> Next, a silicon carbide growth layer was epitaxially grown on the obtained single crystal substrate. Thereby, a silicon carbide substrate was obtained. In the epitaxial growth, ethylene gas and dichlorosilane gas were used as source gases, and the silicon carbide growth layer was obtained by heating at 1000 ° C. for 2 hours.

(Examples 2 to 16)
A silicon carbide substrate was obtained in the same manner as in Example 1 except that the production conditions were changed as shown in Table 1 or 2.

(Comparative Examples 1 and 2)
As shown in Table 1, a silicon carbide substrate was obtained in the same manner as in Example 1 except that the production conditions were changed so that a flat surface was not formed.

(Comparative Example 3)
A silicon carbide substrate was obtained in the same manner as in Example 1 except that the groove forming process was omitted.

2. Evaluation of Silicon Carbide Substrate The density of crystal defects was measured for the silicon carbide substrates obtained in each Example and each Comparative Example. The density of crystal defects was measured by observing the surface of the central portion of the silicon carbide substrate with an atomic force microscope (AFM).

  Next, when the density of crystal defects in the silicon carbide substrate obtained in Comparative Example 3 was 1, relative values of the density of crystal defects in the silicon carbide substrates obtained in each Example and each Comparative Example were calculated. And the calculation result was evaluated in light of the following evaluation criteria.

<Evaluation criteria for crystal defect density>
A: Relative value of density of crystal defects is less than 0.5 B: Relative value of density of crystal defects is 0.5 or more and less than 0.75 Δ: Relative value of density of crystal defects is 0.75 or more Less than 1 x: The relative value of the density of crystal defects is 1 or more.

  As is clear from Table 1, it was confirmed that the silicon carbide substrate obtained in each example had a relatively low density of crystal defects even if the silicon carbide growth layer was thin. From this, it was recognized that according to the present invention, a high-quality silicon carbide growth layer having a thin film thickness can be produced.

DESCRIPTION OF SYMBOLS 1 ... Single crystal substrate, 2 ... Base substrate, 2a ... Lower surface, 2b ... Upper surface, 3 ... Silicon carbide base film, 4 ... Silicon carbide growth layer, 10 ... Silicon carbide substrate, 21 ... Flat surface, 22 ... Groove, 30 ... Second mask, 91 ... crystal defect, 92 ... crystal defect, 93 ... association point, 100 ... single crystal base material, 110 ... first mask, 110 '... mask coating, 120 ... mask base material, 130 ... resist film 221 ... first crystal plane, 222 ... second crystal plane, C ... period, W1 ... width, W2 ... width, α ... angle, θ ... opening angle

Claims (7)

A plurality of grooves including a first crystal face and a second crystal face opposite to the first crystal face on an inner surface and extending in a <110>direction; and a flat surface provided between the grooves; A base substrate comprising:
A silicon carbide underlayer provided on the flat surface;
A single crystal substrate characterized by comprising:   The single crystal substrate according to claim 1, wherein the flat surface is a Si {100} surface.   2. The single crystal substrate according to claim 1, wherein the flat surface is a surface in which a Si {100} plane is inclined at an angle of more than 0 ° and less than 54.7 ° in a <110> direction.   4. The single crystal substrate according to claim 2, wherein an angle formed between the flat surface and the first crystal surface is larger than an angle formed between the flat surface and a Si {111} surface.   The single-crystal substrate according to any one of claims 1 to 4, wherein the base substrate includes silicon, polycrystalline silicon carbide, or diamond. A method for producing a single crystal substrate according to any one of claims 1 to 5,
Preparing a base material with a mask comprising a single crystal base material and a mask provided on a part of the surface of the single crystal base material;
Forming the silicon carbide underlayer on the surface of the single crystal base material;
Etching the single crystal base material to form the groove;
Removing the mask;
A method for producing a single crystal substrate, comprising: The single crystal substrate according to any one of claims 1 to 5,
A silicon carbide growth layer formed on the single crystal substrate;
A silicon carbide substrate characterized by comprising:

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